Abstract
The solitary endoparasitoid, Microplitis ruï¬ventris is considered one of the principal wasps on the cotton leaf moth, Spodoptera littoralis larvae. It has a strange sort of obligate diapause. The data present an evidence of persistent low-level diapause throughout the year and every year that observed under mass rearing conditions. When continuous rearing was done throughout the year at 25°C and 12/12 h L/D, a small portion of the individuals in each large samples of each generation entered diapause. So, a long-timed experiment that repeated three years and collecting dataset that required regular extensive dissections and microscopic observations of emerged diapausing wasps was carried out. This diapause spontaneously terminates after time periods similar each year, showing an evidence of “time memory” in diapausing wasp behavior. The duration of this time period is taken as a proxy of diapause intensity. This had occurred whether the large number of individuals originated in summer from field-collected host larvae or from three successive years of laboratory-rearing parasitoids. Contrary to non diapausing wasps, diapausing females emerge some days early than males. This is the first report of new sort of obligate diapause in diapause induction and termination in M. rufiventris under the same constant rearing conditions. Fecundity of diapaused wasps was diapause intensity dependent. Wasps diapaused for 60-86 days (long diapause) have more number of mature eggs than either of those diapausing for short period (23-57 days) or those of longer diapause (90-165). Key words: Microplitis rufiventris, mass rearing conditions, obligate diapause, diapause intensity, generation effect, fecundity.
Highlights
Microplitis rufiventris Kok. (Hymenoptera: Braconidae) is a specialist endoparasitoid of earlier instars of Spodoptera littoralis (Boisd.), when they still live in clusters near the place of egg deposition
The intact cocoons remaining after initial ceases in each large laboratory samples /month contain pupae in diapause
The percentage in January, February, October, November and December was relatively higher and longer in duration compared with those diapausing in middle generations, showing generation effect
Summary
Microplitis rufiventris Kok. (Hymenoptera: Braconidae) is a specialist endoparasitoid of earlier instars of Spodoptera littoralis (Boisd.), when they still live in clusters near the place of egg deposition. One issue is how the parasitoids diapause, this behavior represents primary part of the life-cycle in many insect species. This wasp behavior remains to be discovered that may offer excellent means for the manipulation of wasp populations to man's advantage, e.g. improve quality control of wasp rearing. It is an adaptations that parasitoids have evolved to overcome stressful periods and to keep in synchrony with the seasonal occurrence of their life requirements (Tauber et al, 1986) It presents an exceptionally clear important problem in insect biology. Knowledge of diapause characteristics in M. rufiventris is crucial for developing efficient mass-rearing techniques and fulfilling its potential as a biological control agent to suppress some noctuid pests in the field. Its main objective is to stimulate further discussion on the important aspect of M. rufiventrisdiapause behavior and “generation effect” in massrearing cultures which in turn might lead to improve quality control in wasp production procedures
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